The present invention is directed toward an electric heating apparatus and, more particularly, to an electric heating apparatus having a resistance wire with at least one of a thermostatic electric current control and temperature sensitive fuse.
Electric heater assemblies having a resistance wire heating element and a thermostatic electric current control device, or thermostat, for controlling the electric current through the resistance wire based on the sensed temperature proximal to the same, are known in the art. Also known in the art are electric heater assemblies having a temperature sensitive fuse, or temperature cutout (xe2x80x9cTCOxe2x80x9d), to disconnect the resistance wire from its current source in response to overheating.
One well known connection and mounting structure for heater thermostats includes a housing enclosing a current control mechanism, with two conducting terminals, or flanges, that extend from the current control mechanism out through the housing. A right-angled two-pronged fork is formed at the distal end of each of the thermostat""s extending flanges. A pair of threaded screw or bolt ends are supported by a corresponding pair of ceramic bushings, each mounted to the frame of the heater assembly, so that the two screws or bolt ends are aligned on the same axis.
The above-described thermostat is mounted by orienting it such that the threaded screws or bolt ends extend through the prongs of the terminal ends, whereupon a nut and associated series of washers is threaded onto each of the threaded screws or bolt ends and tightened. This sandwiches the fork between the nut and a face of the ceramic bushing, which secures the thermostat.
A co-pending application for patent describes a novel method and apparatus which has a reduced parts count and is easier to assemble than the above-identified structure. More particularly, the improved mounting structure uses a thermostat housing with two flanges, each having a through hole extending normal to the extending direction of the flange. A pair of ceramic bushings are mounted to the heater frame. Instead of threaded screws extending through the ceramic bushings, though, a terminal plate extends through each bushing. One end of each terminal plate has a through hole normal to the longitudinal axis of the plate. The other end is formed for crimping onto a wire conductor.
The first thermostat mounting assembly identified above requires complex forked-shape terminal extensions, and typically at least four nuts and at least eight washers. In addition, the assembly typically requires a time consuming manual labor. The invention described by co-pending U.S. application Ser. No. 09/852,947, on the other hand, requires only two screws, two terminal plates, and two support bushings to mount the thermostat.
The invention described by co-pending application Ser. No. 09/852,947, although it provides significant reduction in parts count and is easier to assemble than its prior art, may not be preferred for all uses. One reason is that both it and its described prior art mount use the thermostat terminals as load-bearing members. This necessitates terminals with sufficient structure to support the mass of the thermostat. In addition, both of the above-described structures place a temperature cutout (xe2x80x9cTCOxe2x80x9d) in-line with the thermostat. The first described structure typically secures one wire terminal of the TCO, by crimping or soldering, to one end of an external connection terminal plate which, and secures the other wire terminal of the TCO to the head of one of the screws supported by a ceramic bushing. The structure described in co-pending application Ser. No. 09/852,947 secures one wire terminal of the TCO to one end of an external connection terminal plate, by crimping or soldering, and crimps the other wire terminal of the TCO within the crimping end of one of the terminal plates. In both structures the TCO is suspended between a pair of ceramic bushings.
As can be understood from the description above, it is often necessary to electrically interconnect the resistive heating wire either to a TCO or a thermostat, or both, on the same assembly. The electrical interconnects are generally achieved using flexible electrical wires, having metal terminals attached at one or both ends, the metal terminals connecting to a heating element terminal and to a terminal of the thermostat or TCO.
Various safety requirements exist which specify spacing between electrical conductors, such as between the exposed terminals of the thermostat and the heater support frame. To meet these requirements the existing terminal blocks for TCOs have large and bulky shapes and space-occupying features. Frequently these bulky shapes require that the terminal block have a large size as well, thereby occupying valuable space on the terminal plate.
TCOs generally have wire electrical leads extending from the TCO body. Terminals are typically connected to the wire electrical leads, by one of two methods generally known in the existing art. The first is by soldering or brazing. The second is by resistance welding. Both of these methods, however, have related problems with breaking, especially under mechanical stress. Mechanical stress may occur at the time of assembly, or during subsequent operation. The latter is a particular issue with heating apparatuses, due to the repeated stress cycles of thermal expansion and contraction during operation. The thermal stress places an increased burden on manufacturing quality which in turn, exacerbates any problems relating to inspection.
More particularly, the ability of the soldered, brazed or welded joint to withstand such stress is substantially tied to the quality of the soldering, brazing or welding. Controlling the quality can be difficult, because destructive testing may be the best way to reliably test the quality of soldered or welded joints.
One embodiment of the present invention provides a heater assembly, including a mounting assembly, a temperature-sensitive current cut-off structure, a unitary conducting jumper, a first, second, and third terminal structures, a heating element, and an insulator support structure including a first, second, and third terminal receiving openings formed therethrough. The insulator support structure is releasably and fixedly secured to the mounting assembly. The first terminal receiving opening of the insulator support structure cooperates with the first terminal structure to secure the first terminal structure to the mounting assembly. The second terminal receiving opening of the insulator support structure cooperates with the second terminal structure to secure the second terminal structure to the mounting assembly. The third terminal receiving opening of the insulator support structure cooperates with the third terminal structure to secure the third terminal structure to the mounting assembly. The heating element is releasably and fixedly secured to the mounting assembly, and coupled to the first terminal structure. The unitary conducting jumper is secured to the first terminal structure and to the second terminal structure. The temperature-sensitive current cut-off structure is crimped to the second terminal structure and to the third terminal structure.